Known methods for marinre seismic exploration are based on the emission of acoustic waves in the water from acoustic sources in the form of explosive charges, air guns and the like, whereby the corresponding acoustic signals from the depth are received by means of hydrophones, usually arranged ina seismic streamer which is towed behind a vessel.
This invention provides a completely new concept for such seismic explorations based on the merging of several more or less well-established fields of technology and science today, which gives a high degree of flexibility and makes it possible to design an optimum system for seismic explorations. Some main aspects of this new system are as follows:
New principles in radar technology involving matched radiation (illumination) make it possible to take advantage of apriori information regarding the object, i.e. the structures or subsurface layers under investigation. Based on such information the frequency bandwidth of the system can be narrowed and the sensitivity correspondingly increased. The aim of such a "self-learning" system is to have the appropriate seismic signatures stored in the transmitter unit processor and to structure this in such a way that only two bits of information is required: Is the particular structure present or is it not.
A specific aspect of the invention involves the fact that optimum illumination is achieved by coupling a set of sinusoidal acoustic waves to the wave propagation medium (i.e. water). By using matching networks in the form of resonant cavities, like what is known from microwave circuitry, there can be achieved a very high degree of matching over a narrow bandwidth.
Interaction mechanisms between acoustic and electromagnetic waves are well known in solid state physics and are utilized within electronics as a means of achieving high speed signal processing methods. As examples can be mentioned surface acoustic wave devices for implementation of filters and convolvers. Further can be mentioned opto-acoustic spectrum analysers based on surface acoustic waves in solids.
Thus, the present system is primarily designed for offshore oil and gas explorations and is based on the modern high-technology concept mentioned briefly above.